Enzymatic splitting of fat or oil has been known for a long time and offers, contrary to a pressure splitting mainly practised in the industry, considerable principle advantages. The enzymatic splitting can be performed at normal pressure and, depending on the enzyme and oil or fat, even at room temperature.
It has also been known for a long time that this method of fat splitting is the most gentle one. The technical progress in industrial biotechnology also provided enzymes that are available now and suitable for fat splitting. Such available enzymes are e.g. used in numerous detergents. However, mainly because of the high enzyme consumption, of the very long splitting times and the resulting low efficiency of the enzymatic fat splitting, the enzymatic splitting did not become an industrial alternative method to the large-scale pressure splitting which is well established in industry.
The main problem that occurred in most of the numerous attempts to lower the enzyme consumption is described in the following publications: “Continuous Use of Lipases in Fat Hydrolysis”, M. Bühler and Chr. Wandrey, Fat Science Technology 89/Dec. 87, pages 598 to 605; “Enzymatische Fettspaltung”, M. Bühler and Chr. Wandrey, Fat Science Technology 89/Nr.4/1987, pages 156 to 164; and “Oleochemicals by Biochemical Reactions?”, M. Bühler and Chr. Wandrey, Fat Science Technology 94/No. 3/1992, pages 82 to 94.
The enzymatic fat splitting using enzymes, so-called lipases, as biocatalysts acting on a water/oil mixture is described in these publications. By means of this splitting technique, the oil or fat, respectively, is split into glycerol and free fatty acids. The glycerol migrates into the water phase whereas the organic phase enriches more and more with free fatty acids until, finally, only the free fatty acids remain in the organic phase.
The activity of the used-up enzyme decreases to a great extent with time, and the decrease is mostly independent from the amount of the catalytically converted product. This reduction can be compensated by further additions of enzyme, however, a time-dependently varying enzyme consumption cannot be avoided. In the course of the splitting reaction, the reaction speed or splitting rate decreases more and more, and the enzyme consumption increases. This is due to the fact that the enzymatically catalysed hydrolysis is an equilibrium reaction. With an increasing concentration of glycerol in the water phase and of fatty acid in the organic phase, the reaction speed is slowed down and finally asymptotically approaches the equilibrium concentration. A desired splitting degree near 100%, therefore, can only be achieved after a very long reaction time. This long reaction time unavoidably results in a high loss of enzyme activity. The reaction time can be shortened by lowering the glycerol concentration in the water phase, this, however, implies a low concentration of the glycerol obtainable in the splitting reaction and, due to the higher percentage of the water phase, the water/gylcerine phase has more enzyme dissolved therein that will be discharged with the water phase and cannot be used again.
The enzymatic splitting reaction takes place at the phase boundary between organic and aqueous phase, and only enzyme being present at the phase boundary and triglycerides being present at the phase boundary contribute to or participate in the splitting reaction. With increasing splitting degree, the occupation density or concentration of fatty acids still chemically bonded as glycerides, in comparison to free fatty acids, decreases at the phase boundary so that the reaction is slowed down.
The reaction speed can be accelerated by increasing the interface boundary surface. However, this requires to increase the enzyme amount such that the occupation density or concentration of the enzyme at the phase boundary remains unchanged. The effect of increasing the reaction speed by addition of enzyme is, however, limited. At a maximum concentration, any further addition of enzyme does not contribute to accelerate the reaction. The enzyme consumption is, however, noticeably increased thereby, so that an optimal adjustment of the enzyme quantity and of the surface area of the phase boundary cannot be readily obtained.
Moreover, during a separation step for separating the organic, fatty acid containing phase and the glycerol containing water phase enzyme amounts are discharged and cannot be recovered for further use. It is true that the reaction speed can be increased by increasing the interface boundary surface by intensively mixing the organic and aqueous phase as well as the added enzyme amount, but phase separation, recovery and re-usage of the enzyme become more difficult thereby.
In the above mentioned publications, the enzymatic splitting reaction takes place in a continuous multistage counterflow system of water and oil which is to be subjected to splitting. When separating the aqueous phase containing glycerol and the organic phase containing the split free fatty acids, an intermediate or interfacial layer is generated. This interfacial layer is emulsion-like and contains most of the enzyme. In order to recover this enzyme for the process and to reduce the enzyme consumption, the process according to the aforementioned publication “Continuous Use of Lipases in Fat Hydrolysis” is conducted as follows: first, oil is continuously split in a mixing reactor. The reaction product which, besides free fatty acids, contains water, glycerol, mono- and diglyceride, not yet split oil as well as enzyme, is given into a solid wall bowl centrifuge. The centrifuge is adjusted such that the interfacial layer between the aqueous glycerol phase and organic phase is discharged together with the organic phase.
The organic phase containing the interfacial layer is fed into a second mixing reactor that is supplied with a fresh water/enzyme mixture. The reaction product of the second reactor is fed into a further solid wall bowl centrifuge that is, however, adjusted in such a manner that the interfacial layer is discharged together with the aqueous phase containing glycerol and such that the discharged free fatty acids are free of the interfacial emulsion layer. The aqueous phase is recycled into the first reactor (mixer), so that the enzyme amounts contained in the interfacial emulsion layer are again supplied or back-added to the process. The splitting degree achieved in the second reactor is up to 98%, so that the yield of free fatty acids after distillation of the end reaction product obtained form the second reactor is considerably high. However, even this kind of reaction scheme does not provide a process being actually competitive vis-a-vis the established large-scale pressure splitting process.